This invention relates generally to the field of aerodynamic lifting rotors and, more particularly, is concerned with a rotor that is deployed from a stowed condition to a flight condition when the need arises.
The use of lift generating rotors to retard the descent rate of aerodynamic or non-aerodynamic bodies such as space vehicles or ejection seats has been known for some time. A rotor system of this type is frequently capable of being folded into a configuration permitting storage prior to use. When the rotor is called upon to function, it is pulled from its stowed position and deployed with the aid of other devices such as drogue chutes, explosive actuators or energy storage reservoirs.
In the simpler recovery systems, the rotor is not driven by an auxiliary power supply but instead relies upon the relative flow of air through the rotor system to produce rotation and lift, sometimes referred to drag in this environment, to retard the descent rate of the vehicle.
Three problems encountered in the deployment of a non-powered rotor are the initial deployment and positive preconing of the rotor blades prior to spin-up, blade synchronization in the initial spin-up of the rotor during the early stages of flight and controlling the rotor speed as the suspended vehicle is decelerated to its descent rate. These problems are recognized in U.S. Pat. No. 3,838,940 to Hollrock which discloses in one embodiment a rotor structure which utilizes a torsional spring member which initially spreads the blades from the stowed to flight positions. The patented rotor also employs a flap-to-pitch coupling arrangement provided by unique hinges which aid in controlling rotor speed at the design level. An explosively separable cable interconnects the blade links to restrain the spreading motion of the links so that the coning angle of the blades is limited to an angle no less than a preselected value. After the vehicle has been decelerated by a predetermined desired amount, the cable is severed and rotor speed regulation is terminated.